Floor coating compositions having high durability and removability have historically been obtained by including multivalent metals, such as zinc, which provide crosslinking among the polymer components of floor coating compositions. More recently, however, heightened environmental concern over the use of zinc and other metals in various end-use products, including floor coatings, has shifted the focus to using “greener” technologies. Since the United States Environmental Protection Agency has listed zinc among the 65 Toxic Pollutants and 126 Priority Pollutant list of the Clean Water Act, limits on the amount of zinc that can be discharged down public sewers has been imposed and enforced in the United States. Consequently, there is now a strong demand for zinc-free floor coatings which still have the performance of zinc-containing polishes, and this has driven a need for development of alternative crosslinking technologies that provide the performance that zinc previously provided in such products.
Metal-free polymers first emerged in the 1980′s as an alternative technology for the floor care industry. However, floor coatings containing such metal-free polymers were generally less glossy, less durable and more expensive when compared to the conventional zinc-containing floor polishes. Notwithstanding technological advances in recent years, which are bringing the performance and prices of metal-free polymers to near competitive levels, polymers which deliver equal or superior performance continue to be sought in the floor care industry. Conventional floor coatings continue to contain some zinc and rely on zinc crosslinking to provide the level of high durability and removability demanded by end-users.
Supramolecular polymers, which utilize well-defined hydrogen bonding interactions, have received increased attention as alternatives to typical crosslinking agents such as polyvalent metals. Supramolecular polymers having quadruple hydrogen bond forming moieties provide multiple hydrogen bonding sites in a single functional unit and, as a consequence, provide enhanced stability compared to single hydrogen bonding. Such multiple hydrogen bonds are moderately strong and highly directional, as well as having other desirable properties such as thermoreversibility and responsiveness to external stimuli including pH, solvent polarity, temperature, and concentration. All of these characteristics make supramolecular polymers having quadruple hydrogen bond forming moieties excellent for use in floor coatings in place of, or in addition to, multivalent metals such as zinc to provide floor polishes having excellent durability and removability.
U.S. Pat. Nos. 6,320,018 B1 and 6,803,447 B2 both describe supramolecular polymers containing complementary and self-complementary quadruple hydrogen bonding groups, as well as their synthesis from monomers containing a quadruple hydrogen bonding group and one or more polymerizable monomers. It is mentioned that the quadruple hydrogen bonds of such polymers are much stronger than those in other supramolecular polymers which form only triple hydrogen bonds. There is already a great deal of literature and documentation concerning the synthesis of supramolecular polymers having either 3 or 4 hydrogen bond forming moieties and their relative properties.
U.S. Pat. No. 7,838,621 describes supramolecular polymers and their synthesis where the supramolecular polymers contain multiple quadruple hydrogen bonding moieties as integral parts of the polymeric main chain. Excluded are polymers where the quadruple hydrogen bonding moieties are covalently bonded to one or more silicon-carbon bonds of the polymeric chain.
An object of the present invention is to provide metal-free aqueous coating compositions which are useful in formulating floor coatings having improved durability and removability. This is accomplished by including supramolecular polymers having quadruple hydrogen bonding groups in the aqueous coating compositions, rather than multivalent metals as in the past.